The reproductive system of the female so-iuy mullet Liza haematocheilus (Temminck & Schlegel, 1845) from the Azov-Black Sea basin has been analyzed regarding the season of observation, fish sex and stages of gonad maturity. The median and percentile values which can be used like control values for formation of qualitative characteristic of variational range of certain individual diameters of oocyte based on the empirical median calculated for this individual were calculated basing on the assessment of variational ranges of the large samples of oocyte of trophoblastic growth. It was demonstrated that in Azov-Black Sea basin’s conditions the so-iuy mullet spawning occurs as a single-portioned type except the years with protracted and cold winter. In such conditions is possible a two-portioned spawning.